Composite blocks of adsorptive material, such as adsorbent activated carbon, and polymeric binders, such as ultra high molecular weight polyethylene (UHMW PE), are useful in water filter technology. Carbon block technology, for example, provides comparable functionality to loose bed carbon particles, for example, removal of organic contaminants from water, without the mess or taking up too much space.
In U.S. Pat. No. 7,112,280 to Hughes et al., “gas porous polymer filters and methods of use” are provided. Hughes et al. discusses a method of processing that “involves the vigorous vibration of powdered filter material and polymer until they are firmly compacted into a given space such as a mold cavity. Pockets of air creating unnecessary voids between the particles are reduced in this manner. This achieves the maximum amount of density of materials without external force.” However, vibration can cause fluidization of fine powders, so powders may not fill the mold to the maximum possible density. Vibration has been shown to be highly variable and difficult to control, so that mold filling utilizing vibration is difficult to consistently reproduce. For high levels of fluidization, segregation of particles by size and density can occur when using vibration. Since the Hughes et al. process uses fine media particles and does not compress the block constituents in the molds, relatively larger amounts of binder are required to form a sufficient number of point-to-point bonds to immobilize the particles, in order to produce satisfactory carbon block filters.
Bulk density of a powder varies widely with the way it has been handled. A specific powder will exhibit a maximum uncompressed density. Frequently, a powder is characterized by its maximum uncompressed density because this is a reproducible value. Powders with different compositions and different particle sizes will have different maximum uncompressed density values. ASTM Methods B527, D4164, and D4781 define methods for measuring maximum uncompressed density of a powder. These methods utilize tap filling or tapping.
There is an on-going need to reduce variability in the manufacture of composite blocks, such as filter matrixes. It is also desirable to increase flow through these filters, as well as to increase their capacities for contaminants. Further, there is a need to reduce the amount of binder needed as well as to reduce the amount of scrap material produced.